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Britain is expected to increase the defences of the Falklands over fears that Argentina could launch a fresh invasion of the islands.

Defence Secretary Michael Fallon said land, sea and air defences were being upgraded in the face of a "very live threat" from the government in Buenos Aires.

Defense Secretary Michael Fallon (right). Credit: PA

The move comes amid reports that Russia is working on an agreement to lease 12 long-range bombers to Argentina which could be used to support a renewed attack. Mr Fallon, who is due to set out the Government's plans in a Commons statement later today, said the deal was unconfirmed but that Britain had to take account of any future possible threat.

Media reports suggest the alleged cyber theft is revealed in documents leaked to the German magazine Der Spiegel by former US security analyst Edward Snowden.

The F-35 is a stealth bomber developed by the US-based defence firm Lockheed Martin. The Royal Air Force is among the major customers for the jet.

The Sydney Morning Herald cites one document as saying that the theft amounts to "many terabytes of data" including information about the F-35's radar systems, engines and method for cooling exhaust gases.

BAE Systems, which manages HMNB Portsmouth, has been awarded a £600 million contract while Babcock, which manages Devonport and Faslane, has been given a £2.6 billion deal.

The Royal Navy's warships and submarines will be maintained and repaired as part of the deal, the MoD said.

This huge investment in our naval bases will directly sustain more than 7,500 jobs and skills across the UK and ensure that the Royal Navy's fleet of 56 warships and submarines are in the best possible condition and available for operations.

– Defence Secretary Michael Fallon

The contract will secure around 1,500 jobs at Faslane on the Clyde, up to 4,000 posts at HMNB Devonport and more than 2,000 at Portsmouth.